1. Technical Field
The present invention relates to a filter device in which a sheet-like filter element is installed inside a casing, a manufacturing method for manufacturing the filter device, and a filter element securing tool used for securing a filter element to the above described casing.
2. Background Art
As a filter device of a conventional type, one having the structure disclosed in, for example, Japanese Laid-Open Patent Publication No. 2002-266713, has been proposed. In the conventional configuration described in this publication, a filter element for filtering air that has been taken in is installed inside the casing so as to cross the air flow path. In addition, a fuel adsorbing sheet forming a filter element is installed downstream from the filter element so as to cross the air flow path, in order to adsorb fuel vapor that leaks out from the air intake system of the engine.
A separate resin frame is attached on the entirety of the outer periphery of the above described fuel adsorbing sheet, and a plurality of attachment holes are created in this resin frame. In addition, when the fuel adsorbing sheet is attached inside the casing, the above described resin frame is placed on a support within the casing, and pins of the support are inserted in the respective attachment holes in this resin frame. In this state, the end portions of the respective pins are heated so as to be swaged, and thus, the fuel adsorbing sheet is secured on the support inside the casing.
In the conventional configuration described in this publication, however, it is necessary to prepare a resin frame which is separate from the fuel adsorbing sheet, and then attach the resin frame to the fuel adsorbing sheet, and create a plurality of attachment holes in this resin frame. As a result, the number of parts increases and processing is troublesome, leading to a problem of high manufacturing costs. In addition, a plurality of the above described number of attachment holes are created in the above described resin frame, and therefore, the strength of the resin frame, thus the strength of the outer periphery of the fuel absorbing sheet, may become lower, even in the case where a hard resin is used for the resin frame.
In order to deal with these problems, filter devices such as one disclosed in, for example, Japanese Laid-Open Patent Publication No. 2006-2730 have also been proposed conventionally. In the conventional configuration in this document, the outer periphery of the fuel adsorbing sheet that forms a filter element is thermally pressed so that a plate-like portion is integrally formed with the outer periphery. In addition, when the fuel adsorbing sheet is attached inside the casing, the plate-like portion of the fuel adsorbing sheet is placed on a support inside the casing, and in this state, the plate-like portion is welded to the support through ultrasonic welding or the like, so that the fuel adsorbing sheet is secured on the support inside the casing.
In the conventional configuration of the above described Patent Document 2, however, ultrasonic waves are only applied to the area where the plate-like portion of the outer periphery of the fuel adsorbing sheet and the support inside the casing make contact. Accordingly, the above described support and plate-like portion are joined only in the area where these make contact, and the strength with which the filter element is attached is not satisfactory.